Field of the Invention
In general, the present invention relates to the production of synthetic faujasites, especially zeolites of the zeolite Y type.
Description of the Prior Art
Certain naturally occurring hydrated metal aluminum silicates are called zeolites. Some of these are called faujasites. The synthetic adsorbents of the invention have compositions similar to some of the natural faujasites. The most common of the zeolites are sodium zeolites. Zeolites are useful as detergent builders, cracking catalysts and molecular sieves. Zeolite Y and the zeolite Y of the invention are particularly useful as cracking catalysts.
Zeolites consist basically of a three-dimensional framework of SiO.sub.4 and AlO.sub.4 tetrahedra. The tetrahedra are atoms cross-linked by the sharing of oxygen atoms so that the ratio of oxygen atoms to the total of the aluminum and silicon atoms is equal to two or O(Al+Si)=2. The electrovalence of each tetrahedra containing aluminum is balanced by the inclusion of the crystal of a cation, for example, a sodium ion. This balance may be expressed by the formula Al/Na=1. The spaces between the tetrahedra are occupied by water molecules prior to dehydration.
Zeolite Y may be distinguished from other zeolites and silicates on the basis of X-ray powder diffraction patterns and certain physical characteristics. The X-ray patterns for zeolite Y are described hereinafter. Composition and density are among the characteristics which have been found to be important in identifying zeolites.
The basic formula for all crystalline sodium zeolites may be represented as follows: EQU Na.sub.2 O.Al.sub.2 O.sub.3.xSiO.sub.2.yH.sub.2 O
In general, a particular crystalline zeolite will have values for "x" and "y" that fall in a definite range. The value "x" for a particular zeolite will vary somewhat since the aluminum atoms and the silicon atoms occupy essentially equivalent positions in the lattice. Minor variations in the relative numbers of these atoms do not significantly alter the crystal structure or physical properties of the zeolite. For zeolite Y, an average value for "x" is about 4.5 with the "x" value falling within the range 4.5.+-.0.5. A molar ratio of SiO.sub.2 to Al.sub.2 O.sub.3 of 4.5 or greater is preferred for cracking catalyst use.
The value of "y" is not necessarily an invariant for all samples of zeolites. This is true because various exchangeable ions are of different size, and since there is no major change in the crystal lattice dimensions upon ion exchange, the space available in the pores of the zeolite to accommodate water molecules varies.
The formula for zeolite Y may be written as follows: EQU 0.9.+-.0.2Na.sub.2 O.Al.sub.2 O.sub.3.4.5.+-.1.5 SiO.sub.2.yH.sub.2 O
and wherein "y" may be any value up to 9.
The pores of zeolites normally contain water.
The above formula represents the chemical analysis of zeolite Y. When other materials as well as water are in the pores, chemical analysis will show a lower value of "y" and the presence of other adsorbates. The presence in the crystal lattice of materials volatile at temperatures below about 600.degree. C. does not significantly alter the usefulness of the zeolites as an adsorbent since the pores are usually freed of such volatile materials during activation.
Among the ways of identifying zeolites and distinguishing them from other zeolites and other crystalline substances, the X-ray powder diffraction pattern has been found to be a useful tool. In obtaining X-ray powder diffraction patterns, standard techniques are employed. The radiation is the K doublet of copper, and a Geiger counter or a proportional counter spectrometer with a strip chart pen recorder is normally used. The peak heights, I, and the positions as a function of 2.theta. where .theta. is the Bragg angle, may be read from a spectrometer chart. From these, the relative intensities, 100I/I.sub.o, where I.sub.o is the intensity of the strongest line or peak, and "d" the interplanar spacing in Angstroms (.ANG.) corresponding to the recorded lines are calculated.
X-ray powder diffraction data for sodium zeolite Y are given in Table A. Relative intensity, 100I/I.sub.o and the "d" values in Angstroms (.ANG.) for the observed lines are shown. In a separate column are listed the sum of the squares of the Miller indices (h.sup.2 +k.sup.2 +l.sup.2) for a cubic unit cell that corresponds to the observed lines in the X-ray diffraction patterns.
TABLE A ______________________________________ X-RAY DIFFRACTION PATTERN FOR SYNTHETIC ZEOLITE Y Relative h.sup.2 + k.sup.2 + l.sup.2 d (A) Intensity ______________________________________ 3 14.29 100 9 8.75 9 11 7.46 24 19 5.68 44 27 4.76 23 32 4.38 35 40 3.91 12 43 3.775 47 48 3.573 4 51 3.466 9 56 3.308 37 59 3.222 8 67 3.024 16 72 2.917 21 75 2.858 48 80 2.767 20 83 2.717 7 88 2.638 19 91 2.595 11 108 2.381 6 123 2.232 2 128 2.188 4 131 2.162 3 139 2.099 5 144 2.062 3 164 1.933 2 168 1.910 3 179 1.850 2 187 1.810 2 192 1.786 1 195 1.772 2 200 1.750 4 211 1.704 5 ______________________________________
The particular X-ray technique and/or apparatus employed, the humidity, the temperature, the orientation of the powder crystals and other variables, all of which are well known and understood to those skilled in the art of X-ray crystallography or diffraction can cause some variations in the intensities and positions of the lines. These changes, even in those few instances where they become large, pose no problem to the skilled X-ray crystallographer in establishing identities. Thus, the X-ray data given herein to identify the lattice for zeolite Y are not to exclude those materials which, due to some variable mentioned or otherwise known to those skilled in the art, fail to show all of the lines, or show a few extra ones that are permissible in the cubic system of that zeolite, or show a slight shift in position of the lines, so as to give a slightly larger or smaller lattice parameter.
A simple test described in "American Mineralogist," Vol. 28, page 545, 1943, permits a quick check of the silicon to aluminum ratio of the zeolite. According to the description of the test, zeolite minerals with a three-dimensional network that contains aluminum and silicon atoms in an atomic ratio of Al/Si=2/3=0.67, or greater, produce a gel when treated with hydrochloric acid. Zeolites having smaller aluminum to silicon ratios disintegrate in the presence of hydrochloric acid and precipitate silica. These tests were developed with natural zeolites and may vary slightly when applied to synthetic types.
U.S. Pat. No. 2,882,244 describes a process for making zeolite X comprising preparing a sodium-aluminum-silicate water mixture having an SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of from 3:1 to 5:1, an Na.sub.2 O/SiO.sub.2 mole ratio from 1.2:1 to 1.5:1, and an H.sub.2 O/Na.sub.2 O mole ratio of from 35:1 to 60:1, maintaining the mixture at a temperature of from 20.degree. C. to 120.degree. C. until zeolite X is formed, and separating the zeolite X from the mother liquor.
In U.S. Pat. No. 3,119,659, a kaolin clay and sodium hydroxide are formed into a compact body, dried, reacted in an aqueous mixture at a temperature of from 20.degree. C. to 175.degree. C. until a zeolite is formed. Zeolite X is formed in a reaction mixture having an Na.sub.2 O/SiO.sub.2 molar ratio of 1.5:1, an SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of 5:1, and an H.sub.2 O/Na.sub.2 O molar ratio of 30:1 to 60:1. Zeolite Y is formed in a reaction mixture having an Na.sub.2 O/SiO.sub.2 molar ratio of 0.5:1, and SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of 7:1, and an H.sub.2 O/Na.sub.2 O molar ratio of 20:1 to 40:1.
U.S. Pat. No. 3,920,789 discloses a process for making zeolite Y using elevated temperatures and pressures for the crystallization stage followed by very rapid cooling of the reaction mass.
In U.S. Pat. No. 3,130,007, zeolite Y is formed by preparing an aqueous sodium alumino silicate mixture having a certain composition, maintaining the mixture at a temperature of 20.degree. C. to 125.degree. C. until zeolite Y is formed, and separating the zeolite Y from the mother liquor.
In U.S. Pat. No. 4,016,246, zeolite Y is formed by preparing an aqueous alumino silicate reaction mixture by mixing an alumina component and an Na.sub.2 O component with an active hydrate sodium metasilicate to form a certain reaction mixture, then heating the mixture at a temperature of 20.degree. C. to 120.degree. C. until zeolite Y is formed.
U.S. Pat. No. 4,166,099 discloses a process for preparing crystalline aluminosilicate zeolites, particularly synthetic faujasites such as zeolite Y type, utilizing especially prepared amorphous aluminosilicate nucleation centers or seeds having an average particle size below about 0.1 micron. The latter are prepared by vigorously mixing at a temperature of 35.degree. C. or less a mixture having a molar composition of 13-17 Na.sub.2 O, 1 Al.sub.2 O.sub.3, 12-16 SiO.sub.2 and 300-400 H.sub.2 O and then aging the mixture for two hours or more at 25.degree. C. or less. The mixture of seed and alkaline reaction mixture of alumina and silica is reacted at a temperature of about 60.degree.-150.degree. C. for a period of time sufficient to produce a crystalline zeolite Y.
U.S. Pat. No. 4,164,551 discloses a process for making zeolite Y also utilizing specifically prepared nucleating centers.
U.S. Pat. No. 4,400,366 discloses a process for making a crystalline synthetic faujasite of the zeolite Y type of an exceptionally high crystallinity using a seed quantity of zeolite Y. Such process requires mixing of reactants at a temperature up to about 0.degree. C. and aging period of up to about 16 hours. U.S. Pat. No. 4,436,708 is a modification of such latter process wherein smaller amounts of water are utilized.
Zeolites are useful as molecular sieves and as sequestering agents for calcium and magnesium cations. They are particularly useful in detergent or washing compositions.
One of the primary uses of "Y" type zeolites is as a fluid catalytic cracking catalyst component.
It is a primary object of the present invention to provide a synthetic faujasite of the zeolite Y type which can be prepared using seed quantities of zeolite Y and mixing the reactants at ambient temperature.
It is an important object of the present invention to provide a process for making synthetic zeolite Y which eliminates the necessity of carrying out the reaction at cold temperatures and long aging times.
Another object of the present invention is to provide a simpler and more economical process for making zeolite Y particles using a bulk crystalline seed process.